Discussion in 'Engines' started by Cabo47, May 6, 2020.
Exactly. And run 80% of the factory number not the actual numbers
They stroked the i 6 for the 700 Hp up from 610 Hp by increasing the stroke . 155 to 166 mm ,
because it’s got further to travel for more or less same piston speed it’s WOT was reduced to as said 2200 .
Think bicycle crank , it’s a bit longer and thus produces more torque .
Realise shorter stroked 155 mm WOT @2350 rpm in the Vs .
After it’s annual lift / service it reaches 2275 rpm so about right slightly over or in other words under propped to take into account seasonal fouling etc .
Well, there you go. Thank for the info
Yep, I kinda knew this but forgot from other engines, including SBCs and Outboards.
When we built up SBCs using the 400ci rigs, red line came down.
Built up 3 liter Mercs over the common 2.5Ls, red line came down.
Longer the stroke, red line has to come down,, or else..
I'm not MAN heavy and did not realized your rig had an increased stroke. The joy of these forums, we always learn something new all the time.
But, that MAN 6 lung (IMO) could certainly still take it if needed.
This is especially true of the new v8/1200 HP. There is a large swing in cruise/wot rpms between half fuel or less and full fuel in a few MY's I've run with them installed...….I had to argue with the dealer on one boat and they ended up cutting the props 2" pitch and we picked up 4 knots at cruise and WOT at 80% because motors were able to get into more boost/HP
That's not correct, F42. The stroke has always been 142 mm, for V engines.
It's true that the D2866 had a 155mm stroke, which in your D2876 was increased to 166mm.
But in both cases the red line was at 2200.
On the other hand, in the common rail 730/800, the stroke remained 166mm as in the D2876, but they increased the rated rpm to the same 2300 of all V engines.
Therefore, obviously different stroke alone can't be the reason for the different max rpm.
But don't ask me which were the other evaluations of the chaps in Nuremberg, if any.
To my simple mind, both keeping the same 2200 rpm when the stroke was increased from 155 to 166mm, and also increasing it to 2300 later, had more to see with the marketing thirst for power, which is what sells engines, more than anything else.
After all, they are also part of VW Group now, if you see what I mean...
Just as a last note, in the late noughties MAN realized that they couldn't keep squeezing more power from V blocks originally designed for a much lower output, so they decided to bite the bullet and redesign the crankcase and crankshaft completely.
In this process, the stroke of V engines was increased to the current 157mm, with a correspondingly higher displacement.
So, they are now offering up to 1300 and 2000 hp (always @2300 rpm), respectively on the V8 and the V12.
Which is quite a jump, from 900 and 1360 of the last 142mm stroke V8 and V12.
This did not involve the inline 6 though, whose last power increase was in fact rather limited (800 to 850).
And neither it applies to all the previous generations V engines which we discussed so far.
The only exception is the V8/1200 mentioned by CJ, which is indeed one of the latest 157mm stroke V engines.
So, To the OP Cabo47. Seems to be some serious MAN kids here.
I know I have learned a lot. With support like this on YF at no extra charge, WOW..
Seems the hours on MTBR seems good to better if well maintained.
Lets go water skiing soon..
This power arms race throws up some alarming numbers .
Compare the fuel burns around WOT ....crikey 199 213 L/h with the new versions @ 2300 rpm compared to 136 L/h with old version I have .
So even though the marketing men at boat show stands can brag etc ., think of the stresses inside the cylinders achieving 800 Hp have to burn all that 213 L / h .........
Or worse still 199 for an extra 30 Hp over my 700 s which @2200 burn 136 !!
Moving back to real world usage as I said I set mine @ 80 % load ( because I can ) which burns @ 1780 rpm about 70/80 L/h per side , and according to the chart ^^^ takes out around 630 Hp ...approx .I get a happy 28/29 knots cruise .
So with the newer modals i would not be happy having to run N of 2000 rpm all day long nudging into the 2150 to 2250 to see anywhere near that 800 Hp
That fuel burn is crazy !
May be when new + under warranty but fast fwd 15 years as a used proposition ?
Anyhow @ op your boat prospect seems a excellent match , a 47 with the 800 V8 s ......older fashioned way .
LOL, it's rather that Greek MAN dealer whose website shows those numbers which is a bit crazy, methinks...
They must have made a cut and paste mistake or something, because neither the 199 l/h for 730hp nor the 213 for 800hp pass a basic sanity check.
For your reference, I am attaching the official MAN leaflet, where at page 4 you can see that the right numbers are 145 and 158 l/h respectively, not 199 and 213.
You might find interesting an old trick which I learned many years ago from an old school mechanic, who forgot more about marine diesels than I'll ever learn in another hundred years.
Whenever you want to know how much fuel a diesel engine burns, don't even bother looking at specs.
Just take its rated output in hp, divide it by 5, and you'll get a very decent estimation of its fuel burn in liters per hour at WOT - it's that easy.
And you know what? In the last two decades, I read about all sort of bells, whistles, and claims of improvements in fuel efficiency: from mechanical engines to electronic governors, HEUI and MEUI injectors, common rail - you name it.
But at the end of the day, all these claims always happen to be very close to the "5 hp per each liter/hour" good old rule of thumb.
Which frankly, never fails to make me smile.
Back to the engines discussed so far, let's see what this rough estimate gives us, and cross-check that with the official specs:
V8 800: 800/5 = 160 l/h rough estimate vs. 162 l/h of MAN specs (i.e., a difference of +1.2%);
V10 820: 164 vs. 160 (-2.4%)
V8 1200: 240 vs. 240 (right on the money);
6 700: 140 vs. 136 (-2.8%);
6 730: 146 vs. 145 (-0.7%);
6 800: 160 vs. 158 (-1.2%).
If there is a ballpark rule of thumb which can give more accurate results than this one, I'd be curious to hear about it.
That said, two important considerations on the above numbers:
1) according to MAN, tolerances up to +5% (i.e. well above the previous differences!) can exist also within different units of the same engine model;
2) what these numbers tell us is that all the fuel efficiency claims, from archaic mechanical engines all the way up to the latest and greatest electronic CR like the V8/1200 and the R6/800, are pure marketing BS.
If there is a field where development has achieved meaningful results (emissions aside), it's the power/weight ratio, not power/fuel.
Of course, for any given power, ultimately a lighter boat has less drag and burns less fuel.
An effect which can be somewhat relevant particularly with faster boats.
But this is not an improvement in engine fuel efficiency as such, so to speak.
Here’s a useful “ rule of thumb “ re longevity your Question.
Diesel engines are capable of having a long life when the power to displacement ratio is low. But when they start jacking up the power, beyond what the manufacturer originally intended, that benefit disappears. There is a very simple formula you can apply to estimate service life: simply multiply the cubic inch displacement of the engine times one. The result is the maximum amount of horse power you can have and still expect a reasonable service life. A 6V92 engine is 552 CID; at powers greater than 550, these engines don't last. At 450, they'll go 10 - 15 years easily.
. Now, an 8V71 has a 568 cubic inch displacement; the fact that these engines have a 0.56:1 power/displacement ratio explains why they could run so long.
Conversely, divide the CID by the horse power, and the greater the result UNDER the factor of one (1), the longer engine life you can expect. If you have an engine with an 0.70 CID/HP ratio, then you can expect greater engine hours engine life than one with 1.2 .
Assume it’s correctly propped etc .
@Mapish ....yep thx for the crazy numbers unravel.
I momentarily forgot how good the Greeks are manipulating German numbers .